Fractures of the proximal part of the femur are an important public-health problem and a major source of mortality and morbidity among the elderly. The incidence of fractures of the hip increases exponentially with age, beginning at about forty years for women and forty-five years for men, and rising at eighty years to an aggregate rate of between 20 and 30 percent for women and between 10 and 15 percent for men. Consequently, nearly one of three women and one of six men could sustain a fracture of the hip by the age of ninety years. Lewinnek, G. E., J. Kelsey, A. A. White III, N. J. Kreiger (1980) Clin. Orthop. 152:35-43. This problem is expected to worsen with the projected increase in the average age of the world population. Some researchers have posed the possibility of a two- to three-fold rise in the total number of such fractures by the middle of the next century. Cummings, S. R., J. L. Kelsey, M. C. Nevitt, K. J. O'Dowd (1985) Epidemiol. Rev. 7:178-208.
Hip fracture in the elderly is currently the largest diagnostic group treated in hospital orthopedic departments. Estimates of costs of hip fractures have been calculated for inpatient treatments in the acute phase; however, little is known today about the economic consequences of the entire rehabilitation process. Borquist, L., G. Lindelow, K.-G. Thorngren (1991) Acta. Orthop. Scand. 62:39-48. Thus, prevention of hip fractures can significantly contribute to the reduction of health care costs which are currently of primary concern.
There is considerable controversy as to whether fracture of the hip should be regarded as a disease-related injury resulting from excessive loss of bone, i.e., osteoporosis, or as an accident-related injury due to frequent or severe trauma. See Consensus Conference, NIH: Osteoporosis (1984) JAMA 252:799-802. Although the strong effect of bone density on the risk of fracture of the hip has been widely substantiated, the true influence of this variable is confounded by the increased propensity for falls and injury in the elderly. The combination of both appear to be contributing factors among the elderly. Melton et al. concluded that the combination of reduced skeletal resistance to trauma and increased propensity for falling is an important determinant of risk (Melton, L. J., S. H. Kan, H. W. Wahner, B. L. Riggs [1988] J. Clin. Epiderniol. 41:984-985). As a result, it appears that both loss of bone and trauma are causes of these age-related fractures.
Prior attempts to reduce the incidence of age-related fractures of the hip focused primarily on the prevention or inhibition of the excessive loss of bone associated with osteoporosis. It is now understood that factors in addition to loss of bone play an important role in the etiology of fracture of the hip. Previously, the process of fracture has been poorly understood, particularly with regard to the magnitude and direction of the loads that are present during the impact of a fall. Lotz et al. conducted an in vitro investigation of the loads and energies needed to fracture the proximal part of the femur. They found fracture loads ranged from 778 to 4,040 newtons. Lotz, J. C., W. C. Hayes (1990) J. Bone Joint Surg. 72-A:689-699.
A Danish group of researchers also investigated the role of falls as a cause of hip fractures and concluded that nearly all hip fractures seemed to be caused by trauma. Lauritzen, J. B., B. Lund, Proceedings of the Danish Orthopedic Society, Oct. 27-28, 1989 in Acta. Orthop. Scand. (1990):61 (Suppl.239). Sagittal postural sway has been implicated as a contributing factor in loss of balance, contributing to falls which can potentially result in a hip injury. Jarnlo, G.-B., K.-G. Thorngren (1991) Acta Orthrop. Scand. 62(5):427-434.